The invention relates to a finned-duct heat exchanger serving to transfer heat energy between a liquid flowing through the ducts and between air or gas caused to flow through the spaces between the fins. It relates particularly to a heat exchanger comprising a plurality of parallel closely stacked metal plates, each plate being provided with a plurality of protruding oblong conical collars, wherein the collars of each plate inserted into the collars of the adjoining sheet form continuous parallel ducts extending through the metal plates forming the fins of the heat exchanger. It furthermore relates to a heat exchanger wherein the axes of said oblong ducts are positioned at an angle to the direction of the flow of air or gas with the object of improving heat transfer and, on the other hand, reducing the flow resistance to the gas or air blown through the heat exchanger.
Although the heat exchanger to be described is suitable for any kind of gas flowing between the fins, including air, the expression "air" will be used in the following to describe any gaseous medium flowing through the exchanger, while the expression "liquid" will be used for any fluid, liquid or gaseous, made to flow through the ducts.
The inventor of the present heat exchanger is the owner of an inventor's certificate No. 983431, issued in USSR, disclosing a finned tube-less heat exchanger of the kind which has plurality of oblong finned ducts arranged in parallel rows perpendicular to the direction of air-flow, with their axes alternately inclined at equal angles to the direction of air-flow, thereby creating alternate converging and diverging air channels between pairs of adjoining ducts. Although this arrangement of ducts increases the heat transfer per unit area compared with the conventional finned-tube heat exchangers, it has the inherent drawback that certain portions of the air flow in reverse direction, mostly in the diverging air channel portions from higher to lower pressure zones, as illustrated in FIG. 1 of the drawings. This backflow results in stagnant air flow in the areas at the downstream ends of the ducts, where heat transfer is much lower than along the surfaces with rapid air flow. This type of flow evidently causes higher flow resistance and reduced heat transfer, and it is the main object of the present invention to obviate these drawbacks, as far as possible.
Tests with various arrangements of finned-tube heat exchangers are described in volume 182 of May 1966 of the Transactions of the ASME. These tests were carried out with oblong tubes having their axes aligned in the direction of air flow, and they showed that specific performance was the highest with staggered arrangement of the tubes, especially if turbulators were provided on the fins. These tests are quoted here, since a similar arrangement of ducts is employed in the heat exchanger of the present invention.
The present invention has the above-mentioned objects to reduce flow resistance and to increase heat transfer, and in addition to facilitate production of this kind of heat exchanger by obviating the necessity of sealing the connections between the duct portions of the metal plates by soldering or otherwise, as employed with the conventional type of tube-less heat exchangers.
The design of the heat exchanger according to the present invention is most suitable in the manufacture of radiators for motor vehicles, or of condensors and evaporators in air conditioning units, and in any other equipment designed for the exchange of heat energy between a gas and a liquid.